1. Field of the Invention
The present invention relates to zoom lenses. Zoom lenses according to embodiments of the present invention are suitable for a photographing optical system of cameras, such as video cameras or digital cameras, that use a photoelectric conversion element.
2. Description of the Related Art
When capturing an image with an image capturing apparatus such as a video camera or a digital camera, a photographed image is sometimes degraded in quality (hereinafter simply referred to as “image blur”) due to hand shake or the like. Accordingly, there is proposed an optical system that has the function of preventing such image blur by moving part of lens units constituting a photographing optical system.
U.S. Pat. No. 5,585,966 prevents image blur due to hand shake or the like by moving the whole of a third lens unit of a zoom lens comprises four positive, negative, positive, and positive lens units in a direction perpendicular to its optical axis.
A photographing optical system requires significantly high optical performance along with recent miniaturization of solid-state image pickup elements and significant decrease in pixel pitch. Furthermore, video cameras and digital cameras need to have a color separation prism, an optical low-pass filter and so on between a zoom lens and a solid-state image pickup element. Therefore, such cameras also need to have necessary back focus.
For example, suppose a 3-CCD camera that needs a color separation prism behind a zoom lens. In this case, it is difficult to achieve both of ensuring back focus and high optical performance with the zoom lens disclosed in U.S. Pat. No. 5,585,966.